1. Field of the Invention
The present invention is related generally to a particle beam apparatus, and more particularly to a detector objective for the particle beam apparatus.
2. Description of the Related Art
The electrical properties of modern VLSI microelectronic and opto-electronic components are critically influenced by the geometrical stuctural dimensions of their module components. The observation of strict dimensional tolerances is therefore an indispensable precondition during the manufacture of functional components which have constant physical-electrical properties. This is particularly true when the geometrical dimensions of fine structures, for example, interconnects or fingers of a transducer, are within the micrometer or sub-micrometer range through the use of modern lithographic methods.
All areas of development and manufacture of LSI microelectronic and opto-electronic components, therefore, have an increasing need for high resolution imaging systems to provide a process-proximate inspection and measurement of the generated structures. Scanning electron microscopes have proven particularly well suited for these purposes. Micrometer size and and submicrometer size structrures are capable of being visually evaluated with the aid of scanning electron microscopes so that errors and deviations from the intended patterns are capable of being identified. Also, topographical data such as lengths, widths, heights or angles of inclination are capable of being acquired and interpreted. In all such investigations of microelectronic components using a scanning electron microscope, it must be assured that modifications of the substrate, such as due to contamination or radiation damage, are avoided.
Conventional scanning electron microscopes that achieve a resolution in the range of a few nanometers currently do so by using high acceleration voltages of above approximately 20kV, at which resist structures and the circuits themselves are damaged by the high energy electrons. Also, such high accelerating voltages cause the non-conductive or poorly conducive surface regions of the specimen to become electrically charged. It is standard procedure to apply a metal layer to the surface of the specimen in order to avoid such electrical charges. However, metallization of the specimen deteriorates the resolution and the image quality for such small structures so that it is no longer suitable for investigating microelectronic and opto-electronic components. Also, the applied metal layer disturbs the function of the component and intolerably modifies it so as to prevent further process-oriented handling.